Scale deposition is one of the most serious concerns for the petroleum industry. Scale deposition is the leading cause of declining petroleum production worldwide. Scale removal, scale control and deferred petroleum production costs the petroleum industry millions of dollars each year. Scale is an assembly of hard inorganic crystals that cake perforations, casing production tubing, valves, pumps and downhole completion equipment, thereby clogging the wellbore and preventing fluid flow.
Alkali metal cations such as barium (Ba2+), calcium (Ca2+), and strontium (Sr2+) present in the formation fluids are responsible for scale formation. When these alkali metal cations come into contact with sulfate and/or carbonate anions from the drilling and or stimulation fluid, they precipitate and create scale. Of the three scaling cations precipitated by sulfate, barium sulfate has the lowest solubility (BaSO4=1×10−10 M, CaSO4=5×10−5 M, and SrSO4=3×10−7 M) and is therefore a primary target for the prediction of scale formation, which can be delayed or prevented by using an inhibitor.
Conventional methods for determining scaling cation concentration, in addition to not being well suited for downhole applications, have detrimental flaws which necessitate improvements.